The back and sides of this acoustic guitar are also koa wood, decorated with special abalone highlights. “Martin made two of these special for Norm’s Vintage Guitars, and this is the second one. I tried them both and I could’ve had number one, but I liked number two the best.” The instrument was used on Ryan Adams’ “Love Is Hell.” Keb’ Mo’, who used the guitar on his album “Suitcase,” liked the 45-K so much he later had Martin create a Keb’ Mo’ model based on Porter’s.